Cured epoxysilicone layer membrane for nanofiltration

Abstract

Processes for the preparation of composite membranes are disclosed, as well as the composite membranes obtainable by these processes. The processes employ a step of roller coating a porous support substrate with an essentially solventless coating mixture containing a cationically UV curable compound, which can then be cured in an oxygen-containing atmosphere. The process thereby dispenses with—or greatly reduces the impact of—a number of the prominent processing constraints of prior art techniques, thereby affording a more streamlined and less energetically burdensome membrane manufacturing process.

1 . A process for the preparation of a composite membrane, the process comprising the steps of:
 a) providing a porous support substrate, the porous support substrate having an upper major surface and a lower major surface;   b) providing a coating mixture comprising:
 i. a photoinitiator, and 
 ii. a UV-curable compound bearing one or more groups capable of undergoing cationic UV curing, 
    wherein the coating mixture has a viscosity at 25° C. of 10-1000 cP and comprises less than 50% by weight of a solvent relative to the total weight of the coating mixture, and    and wherein the photoinitiator and the UV-curable compound are such that the coating mixture is cationically curable upon exposure to UV radiation;   c) applying a film of the coating mixture to the upper major surface of the porous support substrate to provide an uncured membrane assembly;   d) subjecting the uncured membrane assembly to UV radiation in an oxygen-containing atmosphere to cause the film of coating mixture to cure;   
       wherein in step c), the coating mixture is transferred from the surface of a rotating first roller to the upper major surface of the porous support substrate. 
     
     
         2 . The process of  claim 1 , wherein the porous support substrate is polymeric. 
     
     
         3 . The process of  claim 1  or  2 , wherein the porous support substrate is formed from one or more polymers selected from the group consisting of polyacrylonitrile, polyetherimide, polyimide, polyaniline, polyester, polyethylene, polypropylene, polyether ether ketone, polyphenylene sulphide, Ethylene-ChloroTriFluoroEthylene copolymer and crosslinked derivatives thereof. 
     
     
         4 . The process of any one of  claim 1 ,  2  or  3 , wherein the porous support substrate is formed from one or more polymers selected from the group consisting of polyacrylonitrile, polyetherimide, polyimide, polyether ether ketone and crosslinked derivatives thereof. 
     
     
         5 . The process of any preceding claim, wherein the porous support substrate is provided on a porous substructure, the porous substructure being in contact with the lower major surface of the porous support substrate. 
     
     
         6 . The process of  claim 5 , wherein the porous substructure is a non-woven material. 
     
     
         7 . The process of any preceding claim, wherein the photoinitiator is a cationic photoinitiator. 
     
     
         8 . The process of any preceding claim, wherein the photoinitiator is an organic salt of a non-nucleophilic anion. 
     
     
         9 . The process of  claim 8 , wherein the anion is selected from the group consisting of BF 4− , PF 6− , SbF 6−  and AsF 6− . 
     
     
         10 . The process of  claim 8  or  9 , wherein the organic salt is a diaryliodonium salt. 
     
     
         11 . The process of any preceding claim, wherein the one or more groups capable of undergoing cationic UV curing are selected from the group consisting of epoxy, oxetane, lactone and vinyl ether. 
     
     
         12 . The process of any preceding claim, wherein the one or more groups that are capable of undergoing cationic UV curing is, or comprises, any one or more or the following moieties: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
         13 . The process of any preceding claim, wherein the UV-curable compound is a siloxane bearing the one or more groups capable of undergoing cationic UV curing. 
     
     
         14 . The process of  claim 13 , wherein the siloxane is a poly(siloxane) or a cyclic siloxane. 
     
     
         15 . The process of any preceding claim, wherein the UV-curable compound has a structure according to formula (I) shown below: 
       
         
           
           
               
               
           
         
       
       wherein
 each R 1  is independently (1-3C)alkyl, 
 each R 2  is independently (1-3C)alkyl or a moiety capable of undergoing cationic UV curing as defined in  claim 12 , 
 each R 3  is independently (1-3C)alkyl or a moiety capable of undergoing cationic UV curing as defined in  claim 12 , 
 a ranges from 1 to 100, 
 b ranges from 1 to 100, 
 with the proviso that at least one R 2  or R 3  is a moiety capable of undergoing cationic UV curing as defined in  claim 12 . 
 
     
     
         16 . The process of any preceding claim, wherein the UV-curable compound is one or more compounds selected from: 
       
         
           
           
               
               
           
         
       
     
     
         17 . The process of any preceding claim, wherein the weight ratio of UV-curable compound to photoinitiator in the coating mixture ranges from 95:5 to 99.99:0.01. 
     
     
         18 . The process of any preceding claim, wherein coating mixture has a viscosity at 25° C. of 10-800 cP. 
     
     
         19 . The process of any preceding claim, wherein coating mixture has a viscosity at 25° C. of 25-650 cP. 
     
     
         20 . The process of any preceding claim, wherein coating mixture has a viscosity at 25° C. of 25-400 cP. 
     
     
         21 . The process of any preceding claim, wherein the solvent that may be present in the coating mixture is an organic solvent. 
     
     
         22 . The process of any preceding claim, wherein the coating mixture comprises less than 40% by weight of a solvent relative to the total weight of the coating mixture. 
     
     
         23 . The process of any preceding claim, wherein the coating mixture comprises less than 25% by weight of a solvent relative to the total weight of the coating mixture. 
     
     
         24 . The process of any preceding claim, wherein the coating mixture comprises less than 10% by weight of a solvent relative to the total weight of the coating mixture. 
     
     
         25 . The process of any preceding claim, wherein the coating mixture comprises less than 5% by weight of a solvent relative to the total weight of the coating mixture. 
     
     
         26 . The process of any preceding claim, wherein the coating mixture comprises substantially no solvent or no solvent. 
     
     
         27 . The process of any preceding claim, wherein the surface of the rotating first roller comprises one or more depressions (e.g. grooves, dimples, notches or furrows). 
     
     
         28 . The process of  claim 27 , wherein the one or more depressions have a total volume of 0.01-100 cm 3  per m 2  of the surface of the rotating first roller. 
     
     
         29 . The process of any preceding claim, wherein during step c) at least a portion of the surface of the rotating first roller is in constant contact with a quantity of the coating mixture contained within a reservoir. 
     
     
         30 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate is metered using a doctor blade or a second roller. 
     
     
         31 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate during step c) is less than 50 g per square metre of the porous support substrate. 
     
     
         32 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate during step c) is less than 10 g per square metre of the porous support substrate. 
     
     
         33 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate during step c) is less than 1 g per square metre of the porous support substrate. 
     
     
         34 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate during step c) is less than 0.60 g per square metre of the porous support substrate. 
     
     
         35 . The process of any preceding claim, wherein the quantity of coating mixture applied to the upper major surface of the porous support substrate during step c) is less than 0.55 g per square metre of the porous support substrate. 
     
     
         36 . The process of any preceding claim, wherein step d) is conducted in an atmosphere containing greater than 1 vol % oxygen. 
     
     
         37 . The process of any preceding claim, wherein step d) is conducted in an atmosphere containing greater than 10 vol % oxygen. 
     
     
         38 . The process of any preceding claim, wherein step d) is conducted in air. 
     
     
         39 . The process of any preceding claim, wherein the cured composite membrane resulting from step d) is subjected to electron beam treatment. 
     
     
         40 . The process of any preceding claim, wherein the process is a continuous process. 
     
     
         41 . A composite membrane obtainable, obtained or directly obtained by the process of any preceding claim. 
     
     
         42 . A composite membrane comprising:
 a porous support substrate having an upper major surface and a lower major surface, and   a polymeric separating layer disposed on the upper major surface of the porous support substrate and in contact therewith,   
       wherein the polymeric separating layer comprises the polymerisation product of:
 i. a photoinitiator, and 
 ii. a cationically UV-curable compound, 
 
       and wherein the mass of polymeric separating layer is less than 10 g per square metre of the porous support substrate. 
     
     
         43 . The composite membrane of  claim 42 , wherein the porous support is as defined in any one of  claims 1 - 40 . 
     
     
         44 . The composite membrane of  claim 42  or  43 , wherein the photoinitiator is as defined in any one of  claims 1 - 40 . 
     
     
         45 . The composite membrane of  claim 42 ,  43  or  44 , wherein the cationically UV-curable compound is as defined in any one of  claims 1 - 40 . 
     
     
         46 . The composite membrane of any one of  claims 42  to  45 , wherein the mass of polymeric separating layer is less than 0.55 g per square metre of the porous support substrate. 
     
     
         47 . The composite membrane of any one of  claims 42  to  46 , wherein the membrane has a molecular weight cut-off (MWCO) in the region of 200-5000 g mol −1 . 
     
     
         48 . Use of a composite membrane as claimed in any one of  claims 41  to  47  for performing a molecular separation process. 
     
     
         49 . The use of  claim 48 , wherein the molecular separation process is a nanofiltration process.